During the lifetime of a patient, it may be necessary to perform a joint replacement procedure on the patient as a result of, for example, disease or trauma. The joint replacement procedure may involve the use of a prosthesis which is implanted into one or more of the patient's bones. In the case of a patella replacement procedure, an orthopaedic prosthesis is implanted into the patient's patella. Specifically, a prosthetic patella implant component is secured to the patient's natural patella such that its posterior surface articulates with a femoral component during extension and flexion of the knee.
To facilitate the replacement of the articulating surface of the natural patella with the prosthetic patella, orthopaedic surgeons use a variety of orthopaedic surgical instruments such as, for example, saws, drills, mills or reamers to resect the posterior surface of the patella and then to prepare the resected surface for fixation of the prosthetic patella implant component.
Common fixation elements for prosthetic patellae include one or more pegs extending out from the bone-facing (anterior) surface to be received in complementary recesses or holes drilled or reamed into the patella. To prepare the patella to receive such a prosthetic patella, the surgeon generally resects the posterior portion of the patella to define a flat surface and then uses a drill guide and drill to drill the hole or holes into the resected surface of the patella. However, it is difficult to hold the patella drill guide stationary against the patella while drilling, particularly when the patella is everted: this surgical step may require one hand to hold the patella, another hand to hold the drill guide and a third hand to drill the holes.
In some prosthetic patella implants, the articulating surface of the prosthetic patella implant component is dome-shaped, as in U.S. Pat. No. 5,593,450. In other types of prosthetic patella implants, the articulating surface has an asymmetric shape to be received and track within the patellar groove in the prosthetic femoral implant component. An example of such an asymmetrically-shaped prosthetic patella implant component is disclosed in U.S. Pat. No. 6,074,425. With such asymmetric patella implants, rotational alignment of the implant impacts the way in which the patella implant tracks in the trochlear groove of the femoral implant. Such asymmetric patella implants typically include a plurality of pegs extending out from the anterior surface to be received in the complementary holes drilled in the patella surface. However, the surgeon typically cannot fully evaluate tracking of the patella implant complonent in the patellar groove of the femoral component until trial patellar and femoral components are in place, which generally requires that the complementary holes be drilled before the trial is placed on the resected patella. If the surgeon determines that the patella trial does not track correctly, there is little opportunity to make adjustments since the mounting holes have already been drilled into the resected patella surface.